William h



WILLIAME poisson, or' ROCHESTER, NEW YORK, AssieNon To HENRY LAMPERT, 0F ISAME PLAGE.

Letters PatentNo. 111,328, dated January 31, 1871.

IMPROVEMENT IN SCROLL-'SAWS.

Thev Schedulerefene to in these Letters Patent and making part of the same.

. I, WILLIAM H; DoBson, of Rochester, in the Vcount)1 of Monroe and State'of New York, have invente'd certain Improvements in Scroll-Saws, of which the following is aspeciication. My invention relates ehiey to the employment of a straining-springof a peculiar character, and inl certain Vdevices for attaching and adjusting the same.

Figure 1 is a iront-view of my invention. Figure 2 is atransverse sectionshowing those partsv to the right of' the dotted linens, fig. 1.

A serions 'diicultywith the various straining de` vices for scrollfsaws now'in use is'the wide'diiference 'in the tension at theextremities of the' stroke, imposf ing? a heavy pressure and consequent wear upon the drive-shaft and connections at the point of greatest tension. y

Most' of such contrivances are, moreover, expensive 4and dific'ult to adjust, and are not readily replaced' vwhen worn ont. v f' I have in a great measure overcomev these objeclions, by formingthestraining-spring A A' of several cords ot' astrong fibrous substance, -sueh as cat-gut, raw-hide, or rubber, or similar tough and slightly elastic material, which are twisted togetherand 'xed atene end to a snspendingeframe,`B,-and at the other to an oscillating segment or arm, a.

A strap,`g, or other flexible connection, attached to the periphery of thelatter, conveys the force of straining-spring to the saw Sibelow.

'4 It will be seen that, when the segment a is located at the eenterof the strainer, `.the section A ot--thelatter must be twisted in an vopposite direction to the section A', in other-words, in placing the spring in position, one section` is twisted right-handed and the other left-handed to a proper degree of tension-before using the saw.

The action of this straining device is obviously very uniform, since the tendency of the twisting mot-ion to slightly stretch the several cords-'of wlnch 1t 1S composed, their elastic reaction taking place onlywithin very small limits.

i lior'the purpose of adjusting the straining-spring, either spirally or longitudinally, the several ,cords are secured in a suitable manner to a short spindle, b,

framepB, and may berevolved by the application of a,

wrench to the nutshaped projection c'. Y

A nut, d, is screwed upon the outer end of the spindie I), bearing against the socket, hymeans of which the tension ofthe 'spring .is adjusted longitudinally.`

The set-screwf retains thesocket c in any desired axial position, abrding means of adjusting the tor.-I

sional .strain of the spring A A. Thus the degree'of f strain necessary .upon the. saw may be regulated at' any time, while the strainer itself can be readily and` cheaply replaced when required.

I tindrit desirable, also, to inclose the several cords i of the strainerin tubes of rubber or some tough.

brous material, which prevents the abrasion and wear consequent upon the constant action of the saw.v

` Itwill beobs'erved that, by means of thesegrnent ct and ilegible connection g, the draft upon the saw is exerted in thesame vertical line, while lthe leverage .of the segment is uniform .during the, whole stroke.`

In the drawing'I have shown the cords-of the strainer-as passing through" openings inthe spindles' b and gudgeons ofthe segment a,

I do not intend to confine' myself to this form of attachment, as other means may be adoptedb'y whichl the wear upon the cords at this point may be reduced.'

Bearings, 71 are attached to the frame B to ,sup-

portthe segment a, retaining it nearly orquite in the,

axial line oi' the spindles b.-

What I claim as my invention is 1. The elastic. straining-'spring A, provided with a rubber guard-cushion, h, for the purposes set forth.

42. The stretching and twisting device b c, constructed and operating substantially as set forth.

W. H. DOBSON Witnesses: l F. H. CLEMENT, GEO'. T. PARKER. 

